It is known that polyurethane foams having usable properties can be made by reacting isocyanates with polyalkylene ether polyols blended with polymer polyols in which polymers such as styrene-acrylonitrile have been polymerized in situ. The properties of foams made in this manner are limited by their use of "cross-linking" and reinforcement from the copolymer. To increase properties through formulation changes in this type of foam, a lower molecular weight per cross-link or higher amounts of polymer must be used. Both of these methods increase the stiffness of the polymer which tends to make the foams harder and less flexible. While increasing certain properties such as tensile strength, these methods lower elongation and resilience. Therefore, to produce an increase in properties with this type of foam and not create excess hardness, it is necessary to use foams of higher density. Plasticizers can be added to the formulation which, if used in the correct amounts, can provide the desired softness. Unfortunately, large quantities of plasticizers are necessary to cause any significant diminution in hardness. Even the most compatible plasticizers bleed (exude) from these compositions at even modest concentrations. Properties are reduced ("fall off") with non-reactive diluents like plasticizers.
Polyurethane-urea foams in which an aromatic diamine has been added are also known. The incorporation of an aromatic diamine produces better properties without an increase in brittleness to the polymer, thus not creating the excess hardness and loss of elongation that an increase in cross-link density produces. However, previously known aromatic diamines that react slow enough to be used in a molded foam process are solids at ambient conditions and must be used at high temperatures during the foaming reaction making processing difficult.